Effects of iron and light availability on phytoplankton photosynthetic properties in the Ross Sea

• Published in: Marine Ecology Progress Series
• Main Authors: Alderkamp, Anne-Carlijn, Dijken, Gert L., Van, Lowry, Kate E., Lewis, Kate M., Joy-Warren, Hannah L., Poll, Willem, van De, Laan, Patrick, Gerringa, Loes, Delmont, Tom O., Jenkins, Bethany D., Arrigo, Kevin R.
• Other Authors: Department of Earth System Science Stanford (ESS), Stanford EARTH, Stanford University-Stanford University, Foothill College, University of Groningen Groningen, Royal Netherlands Institute for Sea Research (NIOZ), University of Chicago, Génomique métabolique (UMR 8030), Genoscope - Centre national de séquençage Evry (GENOSCOPE), Université Paris-Saclay-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Direction de Recherche Fondamentale (CEA) (DRF (CEA)), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université d'Évry-Val-d'Essonne (UEVE)-Centre National de la Recherche Scientifique (CNRS), Graduate School of Oceanography Narragansett, University of Rhode Island (URI), National Science Foundation Office of Polar Programs to K.R.A. (ANT1063592)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: Phytoplankton; Photophysiology; Iron limitation; Ross Sea; [SDV]Life Sciences [q-bio]; Antarc*; Antarctica; Southern Ocean
• Online Access: https://cea.hal.science/cea-04307620; https://cea.hal.science/cea-04307620/document; https://cea.hal.science/cea-04307620/file/m621p033.pdf; https://doi.org/10.3354/meps13000

International audience Waters of the Southern Ocean are characterized by high macronutrient concentrations but limited availability of trace metals and light, often making it difficult for phytoplankton to achieve maximum growth rates. One strategy employed by Southern Ocean phytoplankton in culture to cope with low light and low dissolved iron (DFe) is to enhance light absorption by increasing their antenna size rather than the number of reaction centers, thereby reducing their Fe demand. Here we provide physiological evidence that natural populations of Southern Ocean phytoplankton employ a similar photoacclimation strategy to cope with low ambient DFe concentrations. During a research cruise to the Ross Sea in 2013-2014, we conducted 4 bioassay experiments in which we manipulated light and DFe concentrations and measured changes in phytoplankton biomass, growth rate, photosynthetic parameters, fluorescence parameters, and pigment composition. Phytoplankton responded strongly to DFe additions, exhibiting significantly higher biomass, growth rates, and photosynthetic competency. At low light, the maximum photosynthetic rate (P*max) was significantly reduced and the photosynthetic efficiency (α*) was unchanged compared to the high light treatment, regardless of phytoplankton species composition or DFe concentration. Our data suggest that Southern Ocean phytoplankton have evolved an Fe-saving strategy whereby they photoacclimate to low light by increasing their photosynthetic unit size, rather than photosynthetic unit number, even when DFe is available. It appears this Fe-saving strategy is characteristic of both Phaeocystis antarctica and diatoms, suggesting that it is a common adaptation among phytoplankton taxa that grow under Fe limitation in the Southern Ocean.